From large scale industrial processes, especially those employing chemical treatment or reactions, there can accumulate large amounts of liquid wastes, the treatment of which in many cases, is a burdensome technical expense. According to known processes for the treatment of, for example, oil-containing wastes, after an appropriate prior phase separation of any entrained water, such wastes are burned in order to produce energy. Such a phase separation is therefore expensive from a technical standpoint since in most cases a large liquid volume must be treated and the aqueous phase is separated which still contains about 1 to 4 mg/l of oil phase.
The remaining amounts of the oil phase must be removed from the aqueous phase, before the latter can be discharged into natural waters through drainage ditches. The burning of this oil phase produces exhaust gases containing metal salts therein, including where converted into the corresponding oxides, and spewed into the surrounding air thus harming the environment. Moreover, the additional burdens on the environment from the carbon dioxide or sulfur dioxide produced during burning of the oil phases, separated from wastes can be avoided only at still further technical expense.
The burning of waste products in which halogen-containing hydrocarbons are present, leads to the formation of hydrogen halide-containing waste gases which must be absorbed at considerable technical expense before their release into the atmosphere. The same applies to the formation of unwanted salt solutions which, in turn, must either be treated or transported to the sea.
Acid wastes, such as, for example, dilute acids containing iron sulfate, the so-called green salt, were formerly discharged into the sea resulting in a change in pH value and the undesirable formation of carbonates. The appropriate treatment of these dilute acids can be accomplished only at considerable technical expense and ultimately leads to products which must still be disposed of. To do this, the waste dilute acids which are mostly in the form of emulsions or sludge, are treated with emulsion-breakers and the solids which separate out are separated from the liquid phase by filtration. The resulting residues can then be burned, but care must also be taken that all harmful substances are removed from the resulting exhaust gases before they are discharged into the atmosphere. The separated liquid phase must then, for example, be separated by distillation into an organic concentrate and water. The organic concentrate is burned while the water can first be passed through a layer of solid absorbent before being discharged into a sewer. The spent absorbent must finally be disposed of.
For example, it should be emphasized that by these technologies about 700,000 tons per year of dilute acid with 250,000 tons per year of iron sulfate as well as 35,000 to 90,000 tons per year of halogenated hydrocarbons, have to be removed in a way which is least harmful to the environment. As already mentioned, there is a considerable expenditure of apparatus, plants and energy necessary if pollution of the environment is to be avoided. The same is also true for other pumpable technological wastes.
Furthermore, German published application No. 21 56 315 discloses the storage of wastes in open lagoons after they have been provided with a water-tight and, if necessary, a gas-tight coating. These coatings which consist of bituminous substances or emulsions of plastics in water, and which are poured out in liquid form on the previously solidified bottom of the lagoons and hardened there, can leak due to structural influences so that even with these processes, effects which are harmful on the environment can not be avoided altogether.
There has also been previously proposed a process for the terminal storage of pumpable wastes according to which these liquid wastes are discharged which crystallize at the cavern temperature with the bonding of water of crystallization, or with organic materials which solidify in the liquid phase of the cavern contents or increase their density; or with solids, whereafter the cavern is sealed. The object of this process is to compensate as much as possible for the convergence of the salt cavern by increasing the density of the liquid phase of the cavern contents.
The goal of maintaining a pure environment and also saving raw materials by waste management cannot be achieved for special wastes, which contain in part a high portion of valuable materials, without eliminating the possibility of later recovery involving high technological effort and cost. The task of technology should rather be to treat and store these special wastes so that they can be recovered and utilized providing the highest possible yield. Some of these wastes can already be recycled. For most of the accumulating wastes this possibility has not existed as yet because of the economically non-recoverable treatment costs.
According to the present state of the art, solid wastes are disposed of in abandoned salt mines. After delivery to containers, these are transported underground, removed to salt tunnels and walled in. As far as depositing liquid wastes in abandoned salt mines, only the puddling of the shaft installation is required, which, formerly according to mining laws had to take place with brine. This present practice in the art indeed avoids the above ground treatment of these solid wastes and disposal or elimination by burning or dilution in the sea, but the recovery from the solid deposits is beset with considerable technical effort and costs and is not possible for liquid wastes, if additives are necessary for their solidification.
The state of the art has therefore not moved in the direction of the technically simple phase separation and creation of the technological possibility for recovering wastes for recycling but has as its object the disposal in the sense of terminal storage of such wastes.
In addition, it is known to store petroleum or natural gas in large amounts in salt caverns for re-use. German Patent No. 21 26 823 describes in this connection a process for storage and recovery of gases which are soluble in hydrocarbons. Methane is dissolved in oil utilizing the pressure of the salt water columns which are present above them. The gas is separated from the liquid mixture by expansion in arbitrary cycles and the oil pumped back. This process therefore utilized underground storage in salt deposits for the absorption of gases in hydrocarbon oils and avoids large space containers above ground. This state of the art deals with organic materals, which do not undergo any reaction with the rock salt of the deposit. A homogeneous liquid phase is formed in the deposit with small increase in volume from which the stored phase is recovered by expansion. The oil used as the storage medium is a gas-free fraction of crude oil.
This process is therefore not concerned with any of the several wastes having dissolved substances in the aqueous phase; with an emulsion or suspension of aqueous and oil-containing phases with an arbitrary amount of dissolved or suspended materials such as metal salts; organic compounds; solid sludge of finely divided hydroxide or crystallizates or solid residues.
The gases, such as natural gas, which are recovered by expansion according to the state of the art can be conveyed directly for use as an energy carrier.
Further according to the state of the art, radioactive wastes are deposited underground and terminally stored in mined caverns of salt deposits.
German Patent Publication No. 2 225 664 discloses a process for the deep storage of liquid or oozable radioactive, poisonous wastes. Accordingly, these wastes are mixed above ground with cement or bitumen and "salt gravel" to form a slurry and then pumped into the salt cavern. There the slurry sets up and forms a solid mass. Also according to this process the deposited slurry is converted to an irreversible solid form as a terminal deposit. The depletion of the walls of the salt cavern is prevented by the addition of the crystallized rock salt, the so-called salt gravel. This crystallization quickly dissolves due to its large surface area and converts an unsaturated, aqueous phase into a saturated solution. This state of the art therefore does not teach any recycling of wastes, but is only directed towards terminal storage in salt caverns. This process does not teach the utilization of the dissolving capacity of aqueous solutions for the enlargement of the volume of salt caverns and by this an increase in the storage capacity for wastes, but on the contrary, the prevention of this by the introduction of added crystallizates in the form of salt gravel.
The state of the art has therefore only moved in the direction of the intermediate storage of pure materials or the terminal storage of wastes, which are walled in or solidified.
The teachings of German Patent No. 25 49 313 lead in a similar direction. Accordingly, liquids, especially non-polar intercalation materials are terminally stored in salt caverns and then covered with a gas-tight and watertight coating. Such a medium consists of a mixture of styrene with cyclohexanone peroxide and cobalt accelerators, which harden in the caverns. The coating can also consist of a mixture of polyisobutylene with additions of polyisoprene and/or polybutadiene. The layer of synthetic material thus formed in the salt cavern should exhibit a certain elasticity against solid materials which might fall thereon, so that mechanical harm to the synthetic material layer is largely avoided.
The process of the invention does not require such coatings which hinder the phase separation and recycling of aqueous or oil-containing phases or the finely divided solid materials contained therein.
In view of the considerable effort involved in the known processes for treatment of liquid wastes from chemical processes and in order to safely avoid harm to the environment, the task is rather to find a way to store and treat such wastes in the simplest possible manner which will require little expense and will permit recovery of the valuable materials contained in these wastes without causing harm to the environment by the storage of these wastes.